A process for forming a film (mostly a thin film) on a base such as resin film or semiconductor substrate using any film deposition process is known. A method has been proposed for measuring characteristic values, such as film thickness, of a material produced by means of such a film deposition technique. For example, Japanese Patent Laying-Open No. 2013-019854 (PTD 1) discloses a method for measuring the thickness of a thin film in a measurement chamber in which the humidity is adjusted to be lower than the humidity of the outside, by connecting an oscillator to a detection unit and oscillating the oscillator in the measurement chamber.
A technique for optically measuring characteristics of a material produced by means of a film deposition technique as described above is also known. An optical measurement scheme can be employed to measure not only the film thickness but also a variety of optical characteristic values such as transmittance/reflectance, extinction coefficient, and refractive index.